Papillary Microcarcinomas of the Thyroid with Preoperatively Detectable Lymph Node Metastasis Show Significantly Higher Aggressive Characteristics on Immunohistochemical Examination

<i>Objectives:</i> We recently demonstrated that papillary microcarcinomas with preoperatively detectable node metastasis in the lateral compartment on ultrasonography (clinically apparent metastasis) show worse postoperative relapse-free survival than those with no metastasis or metastasis that could not be detected preoperatively, but was confirmed by pathological examination after surgery (occult metastasis). In this study, we investigated difference in the aggressive characteristics of microcarcinoma of this type from various perspectives. <i>Materials and Methods:</i> We immunohistochemically examined the expression of cell proliferating markers, Ki-67, cyclin D1, p27, and retinoblastoma gene product (pRb), apoptotic markers, single-strand DNA (ssDNA), and metastatic suppressor, kangai-1 (KAI-1) for 19 microcarcinoma patients with clinically apparent metastasis, 14 patents with occult metastasis, and 22 patients without metastasis. <i>Results:</i> Cases of clinically apparent metastasis showed increased cyclin D1 expression together with decreased p27 expression and higher levels of pRb and Ki-67 expression. Furthermore, ssDNA expression was higher and bcl-2 expression was lower in these cases, while KAI-1 expression was significantly reduced. There was no significant difference in the expression of these proteins between cases demonstrating no and occult metastases. <i>Conclusion:</i> These findings suggest that cases of clinically apparent metastasis show significantly higher growth based on cell proliferating activity, apoptosis, and expression of metastatic suppressor than those demonstrating no or occult metastases.